Plasma-induced Damage Research Articles

Plasma-induced damage and annealing repairing in ALD-Al2O3/PECVD-SiNx stacks

We study the effect of plasma-enhanced chemical vapor deposition (PECVD) SiNx process to atomic layer deposited (ALD) Al2O3 films on crystalline silicon surface passivation. The plasma-induced damage on Al2O3 films is affected by the methods of PECVD process (direct or microwave), and the states (as-deposited or annealed) and the thickness of ALD-Al2O3 films. The passivation degradation may be related to the doping of Si, N and H atoms into Al2O3 films during PECVD process, and is mainly manifested in the form of affecting interface defect density rather than negative fixed charge density. In particular, the annealed thick Al2O3 films with direct-PECVD SiNx process show more severe passivation degradation. Anyhow, to the great degree, the passivation quality can be repaired and further improved by post-annealing. Low temperature long time annealing can effectively increase the lifetime of the ALD-Al2O3/PECVD-SiNx stacks, while it cannot be simply replaced by a rapid high temperature firing. By post-annealing repairing, an absolute 0.13% increase in efficiency can be achieved for p-PERC solar cells.

Erratum to “Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance” [Micro and Nano Engineering Vol. 3 (2019) 1–6

Erratum to “Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance” [Micro and Nano Engineering Vol. 3 (2019) 1–6

Effects of plasma shield plate design on epitaxial GaN films grown for large-sized wafers in radical-enhanced metalorganic chemical vapor deposition

Epitaxial growth of GaN films at a low temperature of 800 °C was studied in radical-enhanced metal-organic chemical vapor deposition, focusing on the discharge region of the plasma of a mixture of N2 and H2 gases. The effect of plasma confinement on the growth is crucial for realizing high crystal quality of grown GaN films, owing to the suppression of plasma-induced damage and decomposition of gallium precursors in the gaseous phase. By confined plasma in the discharge region using the plasma shield plates made of metal with multiple small holes effectively, GaN with a relatively flat surface was grown under conditions of higher V/III ratios. Epitaxial growth of GaN films was achieved by modifying the plate design and controlling the high V/III ratio using both the plasma-excitation power and the Ga precursor flow rate.

Chemical bonding structure in porous SiOC films (k < 2.4) with high plasma-induced damage resistance

Abstract The chemical bonding structure of porous low-k carbon-doped silicon oxide (SiOC) films (k Si( CH3)2) is crucial for resistance to plasma-induced damage (PID) and prevention of moisture uptake after the plasma treatment. The mix of di-methyl bonds is believed to be the key to protecting the films from PID because the films retain their hydrophobic characteristics even after plasma treatment. Thus, control of the ratio of di-methyl bonds to mono-methyl bonds ( Si CH3) in the as-deposited SiOC film is necessary. Selection of trimethyl silane as a precursor for film matrix formation resulted in excellent control of this ratio to obtain highly reliable low-k/Cu interconnects for high-performance logic devices.

Electrical Characterization of BEOL Plasma-Induced Damage in Bulk FinFET Technology

Due to the small size of the transistors affected by plasma-induced damage (PID), the electrical characterization of this effect is challenging. In this paper, dc characteristics, breakdown measurements and charge pumping results are combined to extract information about the impact of PID occurring during BEOL processing in an advanced bulk FinFET technology. The effect of PID is visible on the threshold voltage and the transconductance, but not on the gate current and the subthreshold swing, suggesting that fixed charges are responsible for this degradation rather than trap creation. This is confirmed with time-dependent dielectric breakdown measurements. Nonetheless, charge pumping measurements demonstrate that PID increases the density of traps by a factor 1.78, even though the absolute density of traps remain too low to affect significantly the dc characteristics of the transistors.

Effects of BCl3 addition to Cl2 gas on etching characteristics of GaN at high temperature

Gallium nitride films were etched at 400 °C and 20 Pa with a radio-frequency-generated Cl2–BCl3 mixed plasma. While dog-legged profiles were obtained by plasma etching using pure Cl2, straight sidewall shapes were achieved through BCl3 gas addition into the Cl2 plasma by suppressing the plasma-induced damage on the etched surface. Etching by-products containing boron on the etched surface affected the etch rate. Smooth etched profiles were obtained by controlling the redeposition of by-products of boron and chlorine compounds, particularly for substrate temperatures above 230 °C.

Impact of VUV photons on SiO2 and organosilicate low-k dielectrics: General behavior, practical applications, and atomic models

This paper presents an in-depth overview of the application and impact of UV/VUV light in advanced interconnect technology. UV light application in BEOL historically was mainly motivated by the need to remove organic porogen and generate porosity in organosilicate (OSG) low-k films. Porosity lowered the film's dielectric constant, k, which enables one to reduce the interconnect wiring capacitance contribution to the RC signal delay in integrated circuits. The UV-based low-k film curing (λ > 200 nm) proved superior to thermal annealing and electron beam curing. UV and VUV light also play a significant role in plasma-induced damage to pSiCOH. VUV light with λ < 190–200 nm is able to break Si-CH3 bonds and to make low-k materials hydrophilic. The following moisture adsorption degrades the low-k properties and reliability. This fact motivated research into the mechanisms of UV/VUV photon interactions in pSiCOH films and in other materials used in BEOL nanofabrication. Today, the mechanisms of UV/VUV photon interactions with pSiCOH and other films used in interconnect fabrication are fairly well understood after nearly two decades of research. This understanding has allowed engineers to both control the damaging effects of photons and utilize the UV light for material engineering and nanofabrication processes. Some UV-based technological solutions, such as low-k curing and UV-induced stress engineering, have already been widely adopted for high volume manufacturing. Nevertheless, the challenges in nanoscaling technology may promote more widespread adoption of photon-assisted processing. We hope that fundamental insights and prospected applications described in this article will help the reader to find the optimal way in this wide and rapidly developing technology area.

The Study of Plasma Induced Damage on 65-nm Silicon on Thin BOX Transistor

This paper reports new findings about the plasma-induced damage on silicon on thin buried oxide (BOX) transistor. The plasma charge collected by source or drain causes Vth shift, which depends on BOX thickness. In addition, the observation was made that the plasma charge collected by an antenna which is connected to the gate electrode has the same degradation effect as an antenna with the same size but being connected to drain or source. The mechanism of this phenomenon is investigated with various test structures.

Annealing of Proton and Alpha Particle Damage in Au-W/β-Ga2O3 Rectifiers

Vertical geometry Ga2O3 rectifiers were irradiated with 18 MeV alpha particles to fluences of 1–3 × 1013 cm−2 or 10 MeV protons to fluences of 1–3 × 1014 cm−2 and then annealed to establish the thermal stability of the radiation damage. The rectifiers employed Au/W rectifying contacts to achieve the requisite thermal stability to allow for annealing studies. The carrier removal rates were ∼900 cm−1 for the α-particles and ∼200 for the protons. Annealing at 500°C was found to restore the carrier concentration in the α-particle irradiated devices, while 450°C annealing brought substantial recovery of the proton irradiated devices. This is a similar temperature range as established for annealing of plasma-induced damage in Ga2O3, suggesting a common origin of point defects, predominantly Ga vacancies and their complexes. The reverse breakdown voltages and diode on/off ratios are also significantly recovered by annealing after irradiation.

Characterization of the distribution of defects introduced by plasma exposure in Si substrate

Defects in a silicon (Si) substrate induced by plasma exposure—plasma-induced damage (PID)—were investigated using various techniques. The authors performed a comprehensive characterization of plasma induced damages, which will be indispensable for suppressing PID, by precisely assigning the density profile of defects in the region to ∼1016 cm−3. In this study, the Si substrate was damaged using an electron cyclotron resonance plasma system. Cathodoluminescence analysis was used to detect the defects in the damaged Si substrates. The thickness of the damaged layer in the Si substrates was determined to be approximately 1–2 nm by transmission electron microscopy and spectroscopic ellipsometry, while time-of-flight secondary ion mass spectrometry identified the presence of interstitial atoms to a depth of ∼20 nm. Positron annihilation spectroscopy showed that the structural changes related to vacancies interacting with C and F atoms were distributed from the substrate surface to a depth of approximately 130 nm. The authors further verified this finding by a technique using the PID-enhanced dechanneling of As atoms implanted with a projection range of 10 nm. After plasma exposure, the difference between the plasma-damaged and the nondamaged samples in the injected As profiles was identified to a depth of ∼130 nm with a density of ∼1016 cm−3. The comprehensive defect profiling performed in this study provides key guidelines for the introduction mechanism of defects in plasma exposed Si before designing future electronic devices.

Full-Loop Equivalent Circuit Model for Plasma-Induced Damage Simulation

In this paper, a new circuit model is proposed to simulate plasma-induced damage (PID). It includes the two sheaths of the plasma, the blocking capacitor, and the RF power source coupled with the victim device. As a result, this model accounts for both the ac behavior of the plasma and the local voltage imbalance induced by differences in shading factors. The advantage of this approach, compared with the previous works, is that it can yield the waveform impinged by the plasma on the transistor gate, which is known to influence the amount of reliability degradation experienced by the device. Finally, this model is also utilized to elucidate the impact of a parasitic capacitance connected to the transistor gate on the extent of the PID inflicted on the victim device.

Variation-resilient quantifiable plasma process induced damage monitoring

Many wafer manufacturing processes use plasma or other charge-based effects. The resulting currents can damage or destroy MOS gate oxides of transistors in products. This plasma induced damage (PID) can be in form of a reduction of the required lifetime of the devices, which can result in systematic early product failures in the field. PID damage and the resulting reliability reduction can be invisible in zero hour parameter and product tests, which can make it particularly dangerous.Products have to be made robust against PID by antenna design rules determined during technology development and verified in qualification measurements. To prevent early product fails due to unnoticed process excursions, fast wafer level reliability (fWLR) monitoring on the fully processed product wafer is required. The performance of PID fWLR on suitable test structures and the application of the fast diagnostic stresses will be presented. Details on options for data analysis for fast, sensitive and precise process excursion detection will be discussed based on a set of productive fWLR data following this methodology where false alarms are prevented.For some excursions detected by the fast diagnostic stresses the effect on the device lifetimes will be analysed with long term MOS device stresses. The physical reason for this will be discussed in a simple model of the devices' band structures.

(Invited) Low Temperature Thermal ALD TiNx and TaNx Films from Anhydrous N2H4

Titanium nitride (TiN) has been extensively studied in semiconductor devices because of its ideal thermal, mechanical, and electrical properties, along with its ability to act as a diffusion barrier to WF6 during W metal fill. Similarly, tantalum nitride (TaN) is being utilized as a diffusion barrier on SiOCH to Cu, as Cu can readily diffuse, causing device reliability issues. Metal halide precursors are typically preferred over organometallic grown films when there is no concern about substrate etching; however, organometallic-grown films usually contain higher levels of carbon and oxygen contamination, which has been correlated with an increase in film resistivity. Plasma enhanced-ALD TiN has been shown to achieve optimal growth rates with lower contamination at temperatures below 350°C, but the film and underlying substrate can suffer from plasma-induced damage. In this study, low temperature thermal ALD TiNx from anhydrous N2H4 and TiCl4 was performed on SiO2, and the deposited films were studied using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). TaNx films were grown utilizing N2H4 and tris(diethylamido)(tertbutylimido) tantalum(V) (TBTDET) and characterized similarly. In situ XPS was employed to demonstrate pulse saturation during ALD for TiCl4 + N2H4 à TiNx. AFM showed that 40 cycles of TiCl4 + N2H4 at 300°C produces pinhole-free, conformal films. Additionally, the effect of air exposure on TiNx films was studied; O attacked the TiNx film, evidenced by observing a 1.5 eV BE shift of the Ti 2p 3/2 peak. A comparison was made of the TiNx films grown at 300ºC and 400ºC with NH3 vs. N2H4; even at 400ºC there was approximately 2x more O and C and 50% more Cl in NH3 grown films. Furthermore, N2H4 films showed lower resistivities, attributed to lower contamination and likely better nucleation density, especially at 300oC. In situ XPS was also used to study TaNx films grown using TBTDET and N2H4. To study the nucleation on SiO2, an initial TBTDET exposure was performed; the Ta 4d peak position confirmed the nucleation and formation of Si-O-Ta bonds. After subsequent cycles, the Ta 4d peak shifts ~2eV toward lower binding energy upon forming Ta-N bonds. While the films were of extremely high purity with stoichiometry resembling Ta3N5, the N2H4 was unable to reduce the Ta oxidation state from films grown between 100oC and 300oC showing the need for some metals for the use of low oxidation state precursors or a stronger, highly energetic reducing agent. These studies with anhydrous N2H4 show the potential to form high purity barrier layers using low temperature thermal ALD as long as highly energetic reactants are used.

Factor Analysis of Plasma-Induced Damage in Bulk FinFET Technology

In this letter, factor analysis is employed to investigate the hidden dependencies and correlations of plasma-induced damage with other FEOL and BEOL parameters in bulk FinFET technology. First, the test structures are described and the amount of threshold voltage shift resulting from plasma damage is characterized. Next, the different parameters considered are listed and extracted. Finally, they are correlated to the amount of damage inflicted to the transistors using statistical reduction and factor analysis. It is found that the communality of the shift with the parameters considered may partly explain the degraded variability of plasma damaged MOSFET devices.

Optical and electrical characterization methods of plasma-induced damage in silicon nitride films

We proposed evaluation methods of plasma-induced damage (PID) in silicon nitride (SiN) films. The formation of an oxide layer by air exposure was identified for damaged SiN films by X-ray photoelectron spectroscopy (XPS). Bruggeman’s effective medium approximation was employed for an optical model consisting of damaged and undamaged layers, which is applicable to an in-line monitoring by spectroscopic ellipsometry (SE). The optical thickness of the damaged layer — an oxidized layer — extended after plasma exposure, which was consistent with the results obtained by a diluted hydrofluoric acid (DHF) wet etching. The change in the conduction band edge of the damaged SiN films was presumed from two electrical techniques, i.e., current–voltage (I–V) measurement and time-dependent dielectric breakdown (TDDB) test with a constant voltage stress. The proposed techniques can be used for assigning the plasma-induced structural change in an SiN film widely used as an etch-protecting layer.

Incident ion dose evolution of damaged layer thickness in Si substrate exposed to Ar and He plasmas

The effect of ion flux on the formation of a damaged layer in a Si substrate was investigated in detail. An inductively coupled plasma source was used to control the flux (Γion) and energy (Eion) of incident ions. The progressive behavior of the total damaged layer thickness (ddam) estimated by spectroscopic ellipsometry primarily depends on the total ion dose (Dion = Γion × tpr, where tpr is the process time) and Eion. The evolution of ddam then saturates and becomes independent of Dion. The characteristic total ion dose (Ddam) is defined, which distinguishes the progressive and saturation phases. Experimental results suggest that Ddam is estimated to be in the range from 1 × 1016 to 3 × 1016 cm−2, regardless of Ar and He plasmas in the present study. This Dion-dependent behavior was also confirmed by transmission electron microscopy and capacitance–voltage measurements. The interface thickness dIL of the damaged layer was found to be independent of Dion. This result confirms that dIL can be used as a measure of the Eion-dependent plasma-induced damage (PID) for in-line monitoring. The present Dion dependence can be implemented in the conventional PID range theory, particularly, in the designs of high-density plasma sources.

Cold atmospheric-pressure plasma induces DNA–protein crosslinks through protein oxidation

Reactive oxygen and nitrogen species (ROS and RNS) generated by cold atmospheric-pressure plasma could damage genomic DNA, although the precise types of these DNA damage induced by plasma are poorly characterized. Understanding plasma-induced DNA damage will help to elucidate the biological effect of plasma and guide the application of plasma in ROS-based therapy. In this study, it was shown that ROS and RNS generated by physical plasma could efficiently induce DNA-protein crosslinks (DPCs) in bacteria, yeast, and human cells. An in vitro assay showed that plasma treatment resulted in the formation of covalent DPCs by activating proteins to crosslink with DNA. Mass spectrometry and hydroperoxide analysis detected oxidation products induced by plasma. DPC formation were alleviated by singlet oxygen scavenger, demonstrating the importance of singlet oxygen in this process. These results suggested the roles of DPC formation in DNA damage induced by plasma, which could improve the understanding of the biological effect of plasma and help to develop a new strategy in plasma-based therapy including infection and cancer therapy.

Anisotropic selective etching between SiGe and Si

In Si/SiGe dual-channel FinFETs, it is necessary to simultaneously control the etched amounts of SiGe and Si. However, the SiGe etch rate is higher than the Si etch rate in not only halogen plasmas but also physical sputtering. In this study, we found that hydrogen plasma selectively etches Si over SiGe. The result shows that the selectivity of Si over SiGe can be up to 38 with increasing Ge concentration in SiGe. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results indicate that hydrogen selectively bonds with Si rather than with Ge in SiGe. During the etching, hydrogen-induced Si surface segregation is also observed. It is also observed that the difference in etched amount between SiGe and Si can be controlled from positive to negative values even in Si/SiGe dual-channel fin patterning while maintaining the vertical profiles. Furthermore, no plasma-induced lattice damage was observed by transmission electron microscopy for both Si and SiGe fin sidewalls.

Temperature dependence on plasma-induced damage and chemical reactions in GaN etching processes using chlorine plasma

Plasma-induced damage (PID) on GaN was optimally reduced by high-temperature chlorine plasma etching. Energetic ion bombardments primarily induced PID involving stoichiometry, surface roughness, and photoluminescence (PL) degradation. Chemical reactions under ultraviolet (UV) irradiation and chlorine radical exposure at temperatures higher than 400 °C can be controlled by taking into account the synergism of simultaneous photon and radical irradiations to effectively reduce PID.

Expected Failures in 3-D Technology and Related Failure Analysis Challenges

After an introduction to 3-D technology, and through silicon via (TSV)- and stacking options, this paper provides an overview of failures that can be expected in 3-D technology and lists the potential failure analysis (FA) techniques that can be applied to find these failures and the related challenges. Various failure mechanisms and effects that can be expected in TSVs, such as Cu pumping, voids, liner/barrier breakdown, electromigration, mechanical stress impact, Cu diffusion, plasma-induced damage, and the keep-out-zone, are discussed. Also, failures due to backside processing (thinning-induced damage, charging, and Cu exposure) and stacking (misalignment, voids, solder squeeze-out, electrostatic discharge, stress-induced cracking, and delamination) are listed. The importance of mechanical stress and chip–package interaction as a main threat for failures in 3-D technology is highlighted. The FA techniques are not discussed in detail (references are provided). There is a clear need for techniques that can detect failures, such as small (micrometer and submicrometer range) cracks, voids, and delaminated regions (both planar and vertical).